Calibration of one form of top-feed fuel injector is performed by positioning an adjustment tube within the fuel inlet tube to a position that provides a certain preloading of a spring that is disposed between the axially inner end of the adjustment tube and the fuel injector's armature. It is conventional practice to insert a filter cartridge into the entrance end of the fuel inlet tube after the fuel injector has been assembled and calibrated. The purpose of the filter cartridge is of course to filter any particulate material larger than a certain size from the fuel that passes into the interior of the fuel injector.
A typical filter cartridge is generally tubular in shape, comprising a plastic frame that supports a filter medium in the sidewall of the cartridge. The axially outer end of the frame is a circular ring while the axially inner end is an imperforate circular wall. Several axially extending bars of the frame extend between the circular ring and the circular imperforate wall to form radially facing curved windows in the frame. The filter medium is disposed in these windows, fully covering them. A metal band is fitted around the outside diameter (O.D.) of the circular plastic ring at the axially outer end of the cartridge frame to provide a press-fit diameter for press-fitting of the cartridge to the inside diameter (I.D.) of the inlet tube and to provide for the filter medium to be spaced radially inwardly of the inlet tube's I.D. so that a circular annular space is provided between the filter medium and the inlet tube's I.D. The imperforate circular wall at the axially inner end of the cartridge is spaced from the axially outer end of the adjustment tube. After the filter cartridge has been assembled into the inlet tube, fuel entering the inlet tube is constrained to pass first axially through the plastic ring at the axially outer end of the cartridge into the inside of the cartridge, and then radially outwardly through the filter medium to the circular annular space between the cartridge and the inlet tube's I.D. From there the filtered fuel continues axially through the inlet tube and then into the adjusting tube to continue its passage through the fuel injector.
Ideally, calibration of a fuel injector should be conducted after all assembly operations have been completed. Thus, while in the case of the top-feed fuel injector that has just been described it would be advantageous if calibration could be performed after the filter cartridge has been assembled, the filter cartridge inherently blocks access of calibration equipment to the adjusting tube.
The present invention provides a solution that allows the calibration step to be performed after the filter cartridge has been assembled into the fuel injector. This provides the opportunity for a significant consolidation of calibration and final testing procedures, in particular performing final testing while a fuel injector is in a calibration head. This is helpful in reducing the amount of handling of a fuel injector and increasing the through-put of a final test/calibration system. It also offers the potential for significantly reducing the amount of plant floor space that is required for final test/calibration of mass-produced fuel injectors.
Certain functional attributes are also imparted to a fuel injector by embodying the invention in it. A filter cartridge placed in a fuel injector in accordance with the present invention disposes a closed axial end of the cartridge axially outwardly and an open axial end axially inwardly. Upon entering the fuel inlet tube, fuel does not enter the filter cartridge directly, but rather must first pass through a cylindrical annular space between the cartridge and inlet tube and then must make a right angle turn in order to enter the interior of the cartridge by passing through a filter medium on the sidewall of the cartridge. A well is provided at the axially inner end of this cylindrical annular space for collection of particulate material that is filtered out of the fuel by the cartridge. Filtered fuel exits the cartridge via its open axially inner end, and thus there is no accumulation of particulate material within the interior of the cartridge, as could be the case for the prior fuel injector. It can be fairly said that a fuel injector embodying the present invention offers possibilities for improved filtration efficiency. Moreover, because the axially inner end of the cartridge mounts directly on the axially outer end of the adjusting tube, there is no minimum spacing distance between them, unlike the prior fuel injector wherein the fact that the axially inner end of the cartridge is closed mandates a certain minimum spacing distance between it and the axially outer end of the adjusting tube to allow proper flow area for the fuel to pass to the adjusting tube without restriction.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which are accompanied by drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.